This invention relates to a device and method for producing osteotomies in bones experiencing angular deformities, and in particular osteotomies associated with angular deformities of the femur and tibia.
Prior art methods for producing osteotomies to correct angular deformity in a bone mass, such as a femur or tibia, generally require making a large open incision around the deformed site and cutting a wedge, at such site, completely across the deformed bone mass, to initially form two bone pieces. Once the cut has been made in the bone mass and the wedge removed, the bone pieces may be realigned and the angle between the two bone pieces adjusted for corrective purposes. However, because of the invasiveness of the surgery, osteotomy procedures often result in undesirable pain and extended period of immobility for the patient.
In addition to a period of immobility, prior art methods for producing osteotomies have allowed only minimal control of the bone pieces once the bone mass has been divided. For example, as it may be difficult to control the alignment between the two bone pieces of the deformed bone, the correction of the angular deformity may provide clinical results that are unpredictable. Also contributing to the unpredictability of the clinical results is the difficulty in maintaining the bone pieces in approximation after they have been aligned. Moreover, current osteotomy procedures typically involve application of a uniform corrective angle to the bone pieces, regardless of the individual. As individuals vary in height, weight and age, a slight difference in the angle of a deformed bone mass can cause a measurable difference in contact pressure between the articular surfaces of a deformed bone mass and another bone mass (e.g., between a deformed tibia and a femur). A uniform change in the angle of the deformed bone mass for different individuals, therefore, may not result in a sufficient change in the contact pressure between the articular surfaces of the bones, so as to avoid future degenerative problems.
Accordingly, there is a need for a method that produces osteotomies in a minimally invasive, predictable, and measurable manner, in addition to being individualized and reliable, so that the procedure may be performed at an early stage in the course of the disease. Such a method would permit avoidance of severe degenerative changes that frequently accompany current methods for producing osteotomies.
The present invention is directed to systems and methods for producing minimally invasive osteotomies to correct angular deformities of bones in and about the knee. The method of the present invention is accurate, reliable, predictable, measurable, controllable and reproducible. As hereinafter provided, the method is discussed in association with femoral and/or tibial osteotomies. However, it should be appreciated that the method has applications for other bones beyond those bones about the knee.
In accordance with one embodiment of the present invention, the method for producing osteotomy in a first bone having an angle of deformity includes drilling a tunnel through a surface of a first bone at an area about the angular deformity, such that the tunnel drilled is transverse to a plane in which the angle is situated. Next, an oblique cut is made partially across the bone on a surface that is parallel to the tunnel, so as to provide a cut that is at an angle to the tunnel. In an embodiment of the invention, the angle of the cut is such that when the bone is realigned, the contact pressure between an articular surface of the first bone and an articular surface of a second bone approaches a desirable ratio within a physiologic tolerance. Once the cut is partially made across the first bone, the first bone is secured about the cut, for instance, by placing through the tunnel a device which permits bone pieces of the first bone, once the first bone is completely cut, to be maintained in approximation. The amount of angular correction is then determined so that the contact pressure between the first and second bone may be brought to within physiological tolerance. In accordance with an embodiment of the invention, the angular correction is determined by measuring intra-articular pressure between the contact surfaces of the first and second bones. After the amount of angular correction has been determined, the cut is completed across the first bone to form two bone pieces. The bone pieces are then rotated relative to one another about the tunnel, so as to be brought into an alignment which brings about the desirable contact pressure between the first and second bones. The bone pieces are subsequently secured against one another to maintain alignment and close approximation.
In an embodiment of the present invention, the bone pieces are maintained in approximation by the use of a bone anchor assembly having an elongated body for extending across a juncture between the bone pieces. The elongated body includes a distal end and a proximal end. A rigid member is fixedly positioned at the distal end transverse to the body for engaging one bone piece. A locking mechanism is also provided at the proximal end of the body for engaging the other bone piece. To this end, the bone pieces may be pulled against one another between the rigid member at the distal end and the locking mechanism at the proximal end of the device.
Prior to drilling the tunnel through the deformed bone, a support structure of the present invention is preferably affixed along a surface of the deformed bone adjacent the angular deformity. The support structure is designed so that one end attaches to a first end portion of the bone, and an opposite end attaches to a second end portion of the bone. The support structure is also pivotally movable at an area between its ends. In this manner, once the bone pieces are formed, the support structure may maintain the bone pieces close to one another, so that they may subsequently be pivoted into alignment. To secure and maintain the bone pieces in approximation after alignment, a bone anchor assembly of the present invention is positioned through the tunnel and tightened against the bone pieces.